Luminous signs employing a gaseous discharge legend and the methods for making these signs have been disclosed in several patents. In general, these signs are made by using two or three confronting plates where in one or two of the plates is formed a groove or cavity corresponding to the desired legend. The cavity is contiguously attached to a gas entry port incorporating a set of electrodes. In the manufacturing process the cavity is evacuated and a quantity of gas, such as neon, is inserted under pressure and temperature into the cavity through the gas entry port which is then hermetically sealed. The partially pressurized gas is then ionized by applying a voltage across the electrode set. The ionized gas, in turn, causes the legend to illuminate.
The basic problems associated with manufacturing these luminous signs lies in the method used to insulate the crossover point between two overlapping segments of a legend such as in the letter "X" or between any two letters.
This problem and the solution proposed by prior disclosure is discussed in the prior art section below.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however the following United States patents were considered related:
______________________________________ U.S. PAT. NO. INVENTOR ISSUED ______________________________________ 2,852,877 Goebel, et al 23 September 1958 2,158,968 Moffat 16 May 1939 1,937,957 Hotchner 5 December 1933 1,825,399 Hotchner 29 September 1931 ______________________________________
The Gobel patent discloses two embodiments for making a luminous sign. The first consists of a transparent panel and an opaque backing panel. A groove is cut into the confronting face of the transparent panel to form the letters. The groove extends continuously from one end of the plate to the other with a tube inserted in each end into which a gas, such as neon, is introduced to the groove. The spaces between the letters are made nonluminous by inserting an opaque channel shaped shield.
In the second Goebel embodiment, a transparent plate confronts an opaque plate which then confronts a second transparent plate. A groove corresponding to the legend is formed on each plate. The crossover is accomplished by etching or grinding a precision recess into one of the plates at the crossover point. A corresponding precise fitting glass block with a connecting groove is then inserted into the recess where the block acts as an insulator between the two intersecting channels. Due to the precision required between the recess and block, it is extremely difficult and costly to create a good seal. In complex legends hundreds of crossover points may exist requiring hundreds of precisions recesses and blocks adding further to the cost.
The placement of the precision block into its recess can also cause problems when applying and curing adhesives as differences in the coefficients of thermal expansion of the adhesives and glass will cause stresses or cracks when the sign is heated to 450 degrees Farenheit, the temperature considered to be the absolute minimum temperature to decontaminate the neon filled channels to effect optimum illumination. The failure of only one out of number of block/recess in locations becomes evident only after final fabrication and bonding of the lamination. Thus, one small hairline leak in the seal can render the entire sign useless. Additionally, this technique results in the reduction of the cross-sectional area of the gas filled channel as it passes through the blocks, thus causing the luminous intensity and heat output of the gas to increase significantly.
The Moffat patent discloses a method for constructing an incandescent gas sign in which three plates of plastic or glass are hermetically attached in a sandwiched fashion. The front and back plates are flat and confront a middle plate that has a gas containing channel, representing a legend, cut therethrough. A gas receiving opening with an electrode is located on one end of the channel and another electrode is located on the other end of the channel. The electrodes are used to ignite and illuminate the gas.
The first listed Hotchner patent discloses a luminous sign constructed of a light transmitting plate having a light source secured around the perimeter of the plate. The faces of the plate are covered with a reflective film. This film confines the transmitted light within the plate except in those areas where the film has been removed to simulate a legend. Thus, the legend becomes luminous to the eye.
The second listed Hotchner patent discloses a method for fabricating a flat tubeless ionization conductor device. The device comprises two glass plates having legend channels etched in an offset such that the channel may crossover itself without creating a short circuit. This is accomplished by etching each channel with an offset portion that is undercut when formed leaving an overhanging lip extending from the edge over the groove. The opposing lip separates the two superposed portions of the discharge passage at each return bend in the passage. An alternative crossover method is to burrow a tunnel below the surface of the plate such that a bridge of glass remains over the tunnel which may then pass underneath another channel in the legend. Although both methods are possible, they are impractical as they require precision etching which would be very impractical and time consuming if a large number of crossover points were necessary. Further, although it is possible to etch a short tunnel into a glass plate, it is practically impossible to etch a curved tunnel or one of longer length as would be required for complex legends.